SWODY1
SPC AC 181948
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0248 PM CDT SAT JUL 18 2009
VALID 182000Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL/SRN
PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS IN SRN AZ...
EARLIER FORECAST APPEARS ON TRACK WITH BEST POTENTIAL FOR SEVERE
STORMS THIS AFTERNOON ACROSS THE SRN HIGH PLAINS...REFERENCE MD 1613
AND SRN AZ. IF STORMS CAN DEVELOP ALONG THE HIGHER TERRAIN OF NERN
CO...SHEAR AND WEAK INSTABILITY WOULD SUPPORT A SEVERE THREAT.
HOWEVER...18Z RUC FORECASTS DRYING/WEAKENING INSTABILITY ACROSS NERN
CO THIS AFTERNOON...AND AS OF 1930Z...CU HAVE SHOWN LITTLE VERTICAL
DEVELOPMENT ON VISIBLE SATELLITE.
ONLY REAL CHANGE FROM PREVIOUS OUTLOOK WAS TO ADD LOW HAIL/WIND
SEVERE PROBABILITIES ACROSS PORTIONS OF SERN TX AND SRN LA. A BAND
OF THUNDERSTORMS DEVELOPED EARLY AFTERNOON ALONG
DEWPOINT/INSTABILITY GRADIENT FROM NEAR LFK TO POE. ALTHOUGH DEEP
LAYER SHEAR WAS AROUND 20 KT...DUE TO MOSTLY UNIDIRECTIONAL NWLY IN
THE LOWER 3-4 KM. HOWEVER...MUCAPES UP TO 3000 J/KG MAY SUPPORT
PERIODIC STRONG UPDRAFTS...WITH A POTENTIAL FOR BRIEF AND MARGINAL
SEVERE HAIL/WINDS AS THE STORMS SHIFT SSEWD THROUGH THE AFTERNOON.
..IMY.. 07/18/2009
.PREV DISCUSSION... /ISSUED 1116 AM CDT SAT JUL 18 2009/
LARGE UPPER HIGH CENTERED SWRN UT CONTROLS THE CIRCULATION WRN U.S.
WITH AN UNSEASONABLY COLD UPPER TROUGH E OF MS RIVER. ACTIVE NWLY
FLOW PATTERN REMAINS IN PLACE CENTRAL/SRN HIGH PLAINS. ADDITIONALLY
ELY FLOW TO THE S OF UPPER HIGH WILL SUPPORT THUNDERSTORMS MOVING
OFF HIGHER TERRAIN INTO VERY HOT DESERT VALLEYS AGAIN TODAY.
...CENTRAL AND SOUTHERN HIGH PLAINS...
LOW LEVEL MOISTURE HAS MOVED WWD TO FOOTHILLS OF ERN CO/SERN WY.
STRONG EFFECTIVE SHEAR PROFILES REMAIN IN PLACE ACROSS THE HIGH
PLAINS FROM SERN WY SWD TO ERN NM TO E OF UPPER HIGH CENTER. WITH
HEATING...MLCAPES WILL INCREASE TO AOA 1500 J/KG WHICH COUPLED WITH
THE STEEP LAPSE RATES AND 40-50 KT OF SHEAR WILL LEAD TO AN ACTIVE
SEVERE THUNDERSTORM PERIOD FROM MID AFTERNOON UNTIL AT LEAST LATE
EVENING.
SUPERCELL DEVELOPMENT IS EXPECTED GIVEN THE AVAILABLE
SHEAR/INSTABILITY...WITH POTENTIAL AGAIN FOR VERY LARGE HAIL AND
ISOLATED TORNADOES. APPEARS THERE IS AN AREA OF ENHANCED SURFACE
CONVERGENCE E OF DEN WHERE LOW LEVEL CYCLONIC CIRCULATION IS
CURRENTLY NOTED. THIS COULD BE AN AREA OF CONCERN BY MID AFTERNOON
FOR SUPERCELL INITIATION...WITH STORMS/SUPERCELLS INCREASING OFF THE
HIGHER TERRAIN INTO THE ADJACENT PLAINS FROM SERN WY TO NERN NM BY
LATE AFTERNOON.
ALL ACTIVITY WILL DEVELOP S/SEWD REACHING INTO WRN PORTIONS OF OK/TX
PANHANDLE BY EVENING.
...SRN AZ...
WITH ANOTHER VERY HOT DAY LEADING TO STEEP LAPSE RATES WITH LFC/S
ABOVE 600MB...THUNDERSTORMS THAT MOVE OFF THE HIGHER TERRAIN WILL
HAVE POTENTIAL FOR PRODUCING VERY STRONG/DAMAGING WINDS. EXAMINING
PHX/TUS SOUNDINGS SUGGEST THE POTENTIAL FOR STRONG
UPDRAFTS/THUNDERSTORMS WILL BE GREATER WITH SWD
EXTENT...PARTICULARLY GIVEN THE FAVORABLE ELY 20-30KT MID LEVEL FLOW
AT TUS. HOWEVER WITH DCAPES BASED ON MODEL SOUNDINGS AS GREAT AS
2000 J/KG PHX AREA...SUGGEST THAT ANY THUNDERSTORM THAT
MOVES/DEVELOPS INTO THE DESERT VALLEYS WILL HAVE POTENTIAL FOR
POTENT DOWNBURSTS. HAVE INCREASED THE WIND DAMAGE THREAT
ACCORDINGLY ALONG WITH ADDING A SLIGHT RISK MUCH OF SRN AZ.
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